Solid-state NMR Studies of Phenethyl Sulfonic Acid-functionalized MCM−41
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초록
A sulfonic acid–water–silanol system in SO3H-functionalized MCM−41 was investigated using solid-state nuclear magnetic resonance techniques. The proton exchange rate between a water molecule and a silanol group in the S−PE−MCM−41 was determined by analyzing the 1D proton spectra, the proton EXSY spectrum, and 2H spin-lattice relaxation data under various hydration levels. Two kinds of water-bounding sites were found in the S−PE−MCM−41: weakly and strongly bound sites. Over several hours, water molecules bound to the weakly bound sites at the low hydration level migrated to the strongly bound sites. At high temperature, the S−PE−MCM−41 easily lost water molecules weakly bound to the silanol, while the strongly bound water molecules survived. Water molecules that participated in the hydration of the phenethyl sulfonate were involved in the hydrogenbonded silanol mechanism of proton conductivity. This phenomenon contributes higher proton conductivity to the S−PE−MCM−41 by the cooperation of sulfonyl and silanol groups in the proton transfer process, even at higher temperature.
Abstract
A sulfonic acid–water–silanol system in SO3H-functionalized MCM−41 was investigated using solid-state nuclear magnetic resonance techniques. The proton exchange rate between a water molecule and a silanol group in the S−PE−MCM−41 was determined by analyzing the 1D proton spectra, the proton EXSY spectrum, and 2H spin-lattice relaxation data under various hydration levels. Two kinds of water-bounding sites were found in the S−PE−MCM−41: weakly and strongly bound sites. Over several hours, water molecules bound to the weakly bound sites at the low hydration level migrated to the strongly bound sites. At high temperature, the S−PE−MCM−41 easily lost water molecules weakly bound to the silanol, while the strongly bound water molecules survived. Water molecules that participated in the hydration of the phenethyl sulfonate were involved in the hydrogenbonded silanol mechanism of proton conductivity. This phenomenon contributes higher proton conductivity to the S−PE−MCM−41 by the cooperation of sulfonyl and silanol groups in the proton transfer process, even at higher temperature.
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